Database Reference
In-Depth Information
in Step 1. You now pose a question such as this to help you determine whether a constraint
is necessary:
Is there a need to impose some type of limitation on this relation-
ship based on the way the organization functions or conducts its
business?
If the answer is yes, then go to the next step; otherwise, review the next relationship and
perform this step once again. For example, assume you're designing a database for a small
dance studio, and you're working with the relationship between the INSTRUCTORS and
INSTRUCTOR CLASSES tables in
Figure 11.9
.
Figure 11.9. A relationship diagram for tables from a dance studio database
Now, pose a question to help you determine whether the relationship requires a constraint:
Is there a need to impose some type of limitation on this relation-
ship based on the way the dance studio functions or conducts its
business?
Move to the next step if you receive an answer such as this:
Yes, there is. We require all instructors to teach at least one class.
We limit them, however, to teaching no more than eight classes.
You'll use this response as the basis of a business rule in the next step.
Step 3: Define the Necessary Business Rules for the Relationship
Next, define an appropriate business rule based on the response you received in Step 2.
Identify the constraint the response implies and then transform it into a business rule. For
